Microelectromechanical devices (MEMS) integrate electrical and mechanical elements through microfabrication technologies. Most of the current MEMS devices comprise device members that are expected to be electrically connected and mechanically and/or electrically stable. However, the electrical connection may not always be guaranteed due to a variety of reasons, such as erosion from etching and/or patterning processes during fabrication.
Micromirror devices are one type of microelectromechanical devices. A typical micromirror device, such as a device for use in spatial light modulators or in optical signal switches, has a deformable hinge (e.g. a torsion hinge) to which a reflective mirror plate is attached. The deformable hinge and the mirror plate are held relative to a substrate such that the deformable hinge is capable of being deformed; and the mirror plate is capable of being rotated. The rotation states of the mirror plate define the operation states (e.g. ON and OFF states) of the micromirror device.
Rotation of the mirror plate can be controlled through an electrostatic field established between the mirror plate and the addressing electrode disposed proximate to the mirror plate. Such electrostatic field causes an electrostatic torque to the mirror plate; and the electrostatic torque moves the mirror plate in the desired direction. To enable the establishment of the electrostatic field, the mirror plate needs to be electrically connected to the external sources (e.g. electrical voltages). An approach to connect the mirror plate to external sources is to electrically connect the mirror plate to the deformable hinge and deliver external signals from the external source to the mirror plate through the deformable hinge. In this approach, the deformable hinge comprises an electrically conductive layer that is electrically connected to the mirror plate. Because of the active chemical properties of many electrically conductive materials, the electrically conductive hinge layer may have an oxide layer formed thereon during or after the fabrication process. The formed oxide layer can significantly reduce the performance of the conductive hinge layer, which in turn, reduces the performance of the hinge.
As an example, TiAlx is often used as an electrically conductive hinge layer of a micromirror device. The TiAlx hinge layer may have formed thereon a non-conductive oxide layer during fabrication. Such oxide layer may produce organometallic materials when exposed to photo processing, such as patterning using a photoresist material. The produced oxide layer and/or the organometallic materials, as well as other possible contaminates may not have been removed during etching or cleaning of the micromirror device. As a consequence, these materials are left with other device members of the micromirror device after releasing.
Therefore, it is desired to protect the electrically conductive layer of a MEMS device, while maintaining the desired electrical conductivity between particular device members of the MEMS device.